The present invention relates to image sensing using a solid-state image sensing apparatus. Particularly, this invention relates to image sensing using a solid-state image sensing apparatus with a function of shifting light from an object to shift pixels for enhancing resolution equivalent to the resolution of a solid-state image sensing apparatus having a larger number of pixels.
Video cameras with a digital still-photographing function and digital still cameras install a solid-state image sensing apparatus with a function of shifting light incident to a solid-state image sensing device from an object to shift pixels for enhancing resolution equivalent to the resolution of a solid-state image sensing apparatus having a larger number of pixels (called a pixel-shifting function hereinafter).
Illustrated in FIG. 1 is a timing chart of exposure and reading for a solid-state image sensing device with such a pixel-shifting function. As illustrated in EXPOSURE TIMING, exposure of a charge-coupled device (CCD) as a solid-state image sensing device for the first frame starts at time t11, charges that have been stored on the CCD are discharged at time t12 by an electronic shutter that is ON (opened) at timing as illustrated in ELECTRONIC SHUTTER TIMING, and exposure starts again.
For progressive-scanning, charges stored on pixels are once transferred to a vertical transfer register at time t13. Then, at timing a1 as illustrated in READ TIMING, the charges are transferred to a horizontal transfer register and read out. The period from time t12 to time t13 is an exposure period c1. Charges stored on the CCD for this period are output as an image signal for the first frame.
Exposure of the CCD for the second frame starts at right after time t13, charges that have been stored on the CCD are discharged at time t14 by the electronic shutter that is ON (opened) at timing as illustrated in ELECTRONIC SHUTTER TIMING, and exposure starts again. Charges stored on pixels are once transferred to the vertical transfer register at time 1t5. Then, at timing a2 as illustrated in READ TIMING, the charges are transferred to the horizontal transfer register and read out. The period from the time t14 to time t15 is an exposure period c2. Charges stored on the CCD for this period are output as an image signal for the second frame.
Before exposure for the second frame, light incident to the CCD from an object is shifted by one line in the vertical direction as illustrated in PIXEL-SHIFT TIMING.
The image signals read out at timing a1 and a2 illustrated in READ TIMING for the first and the second frames are combined by signal processing 25 and output for enhancing resolution equivalent to the resolution of a solid-state image sensing apparatus having a larger number of pixels.
Illustrated in FIG. 2 is another timing chart of exposure and reading for a solid-state image sensing device with a pixel-shifting function.
The higher the shutter speed, the shorter the exposure period for each frame as illustrated as c3 and c4 compared to the periods c1 and c2 shown in FIG. 1. This causes delay in charge storing starting time to the CCD as time t16 and time t17, compared to time t12 and time t14 shown in FIG. 1. Charges are, however, read at time t13 and time t15 at which frames terminate, the same as shown in FIG. 1.
Solid-state image sensing apparatus as described above perform charge-reading when each frame terminates, thus resulting in displacement of image in time as illustrated in “d” in FIGS. 1 and 2, even in photographing with high-speed shutter for avoiding blurry photos.
A shutter speed for CCDs as illustrated in FIG. 2 higher than that illustrated in FIG. 1 will not cancel the displacement of image “d” as discussed above due to a fixed shutter speed for CCDs.
Solid-state imaging apparatus with a pixel-shifting function having a large displacement of image “d” as discussed above produce blurry photos with a deteriorated image quality.